By Whitney Cranshaw, Colorado State University Cooperative Extension
Entomology Specialist

Vinegar flies, also known as small fruit flies, commonly develop in overripe or
decaying fruit and vegetable matter. They are minute, light brown flies with
orange-red eyes and rarely are they found very far from the fruit bowl. Numbers tend to
build in late summer. If conditions are suitable and food is present, they may breed
indoors.

Although associated with fruit, developing vinegar flies actually feed on yeasts. To
eliminate a vinegar fly problem, use up overripe fruit, refrigerate it or discard it. At
the same time, give attention to other breeding sites. Vinegar flies may, for example,
breed in the moist residue that remains in the bottom of beer bottles or soft drink cans,
as well as in other areas where moist organic matter allows for yeast growth. After all
such food sources are removed, some residual adults may remain for a week or so, but
ultimately will die out.